Avoid windows crate dependency in implement and interface macros

[kennykerr]

The implement and interface macros used for COM support don't need to depend on the windows crate itself, but as a consequence of how proc macros inject code it can get a little awkward since any dependencies that may be injected are the responsibility of the calling crate to provide. Still, I think this is cleaner and allows these macros to be used in more scenarios. The only real issue you may encounter when upgrading is the need to add an explicit dependency on the windows-core crate, if you don't already have one.